Antioxidant and Antimicrobial Studies of Some Hemi-parasitic West African Plants

Abstract

The study investigated the antioxidant and antimicrobial activities of some West African hemi-parasitic plants, which comprised Tapinanthus bangwensis (TB), Tapinanthus globiferus (TG) and Globimetula braunii (GB), used in Nigerian ethnomedicine for the management of skin and other microbial infections. This was with a view to determining the most active plant extract and fraction. The leaf and stem of each plant was separately air-dried, powdered and macerated in ethanol-H20 (8:2). The extracts were subjected to in vitro antioxidant tests such as 2,2-diphenyl-1-picrylhydrazyl (DPPH), ferric reducing antioxidant power (FRAP), Fe2+ chelating ability (FIC) and total antioxidant capacity (TAC) assays, with L-ascorbic acid, quercetin and ethylenediaminetetraacetic acid (EDTA) as positive controls. The antimicrobial test was carried out using micro-broth dilution method against reference strains of methicillin-resistant Staphylococcus aureus (MRSA), Bacillus subtilis, Escherichia coli, Pseudomonas aeruginosa and Candida albicans, where ciprofloxacin and ketoconazole were the positive controls. An activity-guided fractionation approach was adopted in the study. The most active GB leaf extract was fractionated to obtain n-hexane, dichloromethane, ethylacetate, n-butanol and aqueous fractions, and were subsequently tested. The results showed that the extract of GB leaf demonstrated the highest bioactivities with inhibitory concentration (IC50) of DPPH at 31.21±1.11 µg/mL, FRAP value of 109.30±0.76 mg AAE/g, TAC value of 178.15±3.54 mg AAE/g and MIC of 5.0 – 10.0 mg/mL. The Ethylacetate fraction of GB leaf demonstrated the highest bioactivities, which were four-times, thrice and twice better than its GB leaf extract in the DPPH, TAC and antimicrobial studies respectively. The EtOAc fraction (IC50 = 8.58±1.39 µg/mL) was comparable (P > 0.05) in antioxidant activity with quercetin (IC50 = 7.72±0.88 µg/mL). The EtOAc fraction also exhibited broad-spectrum antimicrobial activity with inhibitory concentration of 1.25 mg/mL against MRSA and C. albicans. In conclusion, the extract of G. braunii leaf demonstrated considerable bioactivities and the moderately polar EtOAc fraction was the most active fraction; hence, validates the folkloric use G. braunii leaf as a remedy for microbial infections.